Partial rotation or arcuate positioners are known in the prior art and typically employ arcuate rolling bearings in which balls, spaced by cages, roll in opposed arcuate gothic arch shaped tracks allegedly providing a four-point contact surface. Current designs typically comprise stages mounted for limited rotation and controlled by a guide arrangement, such as arcuate dovetail mating grooves or arcuate cross-roller arrangements with cooperating v-grooves. Dovetail mating arrangements, however, do not provide negligible eccentricity coupled with smooth sensitive action and is inadequate, for example, for fiber optic alignment, and while cross rollers address such problems, cross rollers are difficult to assemble and align and are relatively expensive, even for critical fiber optic alignment applications.
In a related problem of the prior art, the goniometer rotor plate to which a device or instrument to be rotationally positioned is mounted is typically mechanically coupled to the goniometer base, which also serves as a reference plane, by means of a gear mechanism, such as a screw thread or pinion gear and a toothed rack, by which the angle of the rotor plate relative to the base is adjusted. Due to irregularities in, for example, the shape of or mechanical relationship between the toothed rack and the pinion gear or screw thread or irregularities or imperfections in the shape of the gear and rack teeth, however, there is typically a degree of slippage, backlash or errors in the positioning and rotation of the rotor plate with respect to base. These mechanical tolerances often result in an unacceptable degree of error in positioning the rotor plate and often allow the rotor plate some degree of movement independently of the rack and gear mechanism, which is again typically unacceptable